This invention relates to an apparatus and method for attaching a fluid dispersion device to a fractionation tray. It particularly pertains to an apparatus to minimize the time and cost needed for assembling the fractionation tray with valve devices for use in distillation columns and other related apparatus in the separation between two fluids such as a vapor and a liquid.
Distillation is a process in which a fluid, typically a vapor and a liquid mixture of two or more substances is separated into its component fractions of desired purity, by the application and removal of heat. Distillation columns are designed to achieve this separation efficiently. One type of column which is used in distillation is a tray column where a number of trays of various designs hold up the liquid to provide better contact between process vapor and process liquid which leads to better separation.
Basic distillation begins from a top portion of a column to a bottom portion of the column. Heavier process liquid flows down the column while lighter process vapor ascends up the column. The main components of distillation columns include a vertical shell, where the separation of the process vapor and liquid substances occurs, and column internals, such as fractionation trays or packings. The column internals increase and enhance the separation between the process vapor and liquid. The internal configurations of the column internals such as tray spacing, column diameter, placement of assemblies to enhance flow increase the efficiency and thereby lead to a lesser requirement of energy.
In a typical distillation column arrangement, a number of horizontally oriented surfaces or fractionation trays are mounted in a sealed, vertically oriented vessel known in the industry as a column or tower. Each of the trays may contain numerous openings which enhance the separation of the vapor and liquid. The simple openings allow the lighter process vapor from below the fractionation tray surface to flow through the tray to interact with the heavier process fluid above. However, these simple openings and holes permitted the vapor to shoot or jet upward through the fractionation tray at lower fluid flow rates and flood the tray. This led to inefficient fluid exchange and separation and a reduction in efficiency and capacity of the entire distillation column.
To prevent flooding of the fractionation tray section, the openings were designed to have a partial cover or sieve above each opening. The sieve tray designed by this method prevented flooding by directing the lighter vapor into a more lateral direction. However, the sieve tray introduced a new problem of jet spray across the fractionation tray whereby the vapor would shoot in a lateral direction across the tray. This also reduced the efficiency of the tray and column. Additionally, the sieve tray was more expensive to manufacture as the sieve tray openings were machined from the same surface of the fractionation tray by punching or molding. No alterations could be readily made after construction of the sieve tray. Thus, if a portion of the sieve tray were damaged, the entire tray would need to be replaced.
Another prior art fractionation device used to enhance the vapor fluid interaction was the bubble cap. A bubble cap tray has a support riser over each opening and a cap that covers the riser. The cap is mounted so a space exists between the riser and cap to allowed the passage of the process vapor from below the tray through the bubble cap to interact with the process liquid. The vapor rises through the rise and is forced downward by the cap. Slots in the cap allow the vapor to interact or "bubble" through the liquid flowing across the tray. However, the bubble cap tray had a lower efficiency and was expensive to maintain and operate. The complicated structure also increased the costs of replacement and manufacture.
To provide an alternative to sieve and bubble caps, valve trays were developed to provide a more efficient fluid exchange and separation. The fractionation tray openings were covered with liftable cover plates. The cover plate would "float" above each tray opening. The lighter fluid from below the tray lifted the plates in a upwardly sliding motion to create a flow area for the passage of vapor. The lifting plate directed the vapor to flow horizontally through the liquid on the fractionation tray surface. The increased contact between the vapor and liquid provided better interaction and separation between the process fluids. The cover plates are typically called valves.
Various valve designs have been developed to insert the valve into the fractionation tray openings. The cover plate is attached to downward projections or legs and inserted into the tray openings. During installation, a person skilled in the art would insert the valve device into the tray opening. Another person would be required to be at or near the underside of the fractionation tray to bend or turn the legs whereby the valve would not become detached from the opening during vapor lifting and floating. Other prior art devices utilized locking mechanisms such as retainer rings to limit the lifting of the valve above the tray surface.
However, in a typical valve tray, hundreds of valves may be installed on the fractionation tray in the hundreds of openings. This is a time consuming process to have two installers insert each valve and then lock it into place by mechanical force or devices. Additionally, the cover plates of prior art valves could become stuck in a closed position to the fractionation tray surface under a vacuum pressure because of non-uniform mechanical bending and the free moving retainer rings. The non-uniform bending could also cause the valve to become stuck in an "open" position where the cover plate is locked above the fractionation tray surface. Weeping or the seepage of fluid to the tray surface below could occur leading to a greatly reduced efficiency and column.
Accordingly, there is a need for a fractionation valve which can be easily inserted into the fractionation tray openings. The fractionation valve should be easy and simple to construct while retaining enough strength to operate in the high pressure vapor and liquid environment. The fractionation valve should also move freely within the tray opening such that vapor flowing from below the tray can easily lift the valve at lower vapor pressure while preventing the valve from being suctioned closed.